Luminescence and electronic structure of the self-trapped exciton in alkali fluorides and chlorides

Luminescence of the self-trapped exciton in alkali halides is analysed on the basis of recent theoretical works. It is shown that the short-lived σ-band originates from an orbital state which is distinct from that of the much studied triplet state. Luminescence from the lowest orbital state consists of two components and this gives rise to the peculiar behaviour of the π-band, as has been reported recently by Purdy and Murray for KCl.